Abstract Untreated opioid use disorder (OUD) is a continuing public health emergency in the United States. OUD is associated with significant morbidity and mortality, including overdose death. Buprenorphine is an effective treatment for OUD, but most individuals who need such treatment do not access it. Public STD clinics are high-volume, episodic care medical settings that serve a high-risk population, often on a walk-in basis. STD clinic patients have high prevalence of OUD and health-risking behaviors. This proposed study, entitled Opioid Use Disorder Treatment Linkage at STD Clinics using Buprenorphine (OUTLAST-B), will examine OUD treatment linkage strategies for opioid-dependent patients seeking services at public STD clinics. This three-arm, parallel randomized clinical trial (RCT) will compare Usual Care (UC), vs. referral via Patient Navigation (PN), vs. Patient Navigation with STD-clinic initiated buprenorphine (PN+BUP). The UC Arm will include standard services at the STD clinic. The PN Arm will include all UC Arm services, with the addition of a Patient Navigator who will assist the participant in selecting a community OUD treatment program, facilitate an intake appointment, help to resolve barriers and coordinate OUD treatment entry, and support early retention in OUD treatment. The PN+BUP Arm will include all PN Arm services, with the addition of meeting with the STD clinic?s buprenorphine-waivered provider (typically a nurse practitioner) to initiate buprenorphine treatment, as a bridge until successful transfer to OUD treatment in the community. Research assessments consisting of a structured interview battery and biomarkers for drug use and STDs will be conducted at baseline, 3-, and 6-month follow-up. Selected outcomes will be examined through 12-months via health record linkage methods. The study will examine participant outcomes in the domains of: (1) OUD treatment entry and retention, (2) Opioid use and related problems (including fatal and non-fatal overdose), and (3) HIV/STD-related outcomes. This innovative study could identify new approaches to engaging a high-risk patient population in OUD treatment. The study could have high impact because findings could be scaled to STD clinics throughout the nation, spurring novel integration across two traditionally separate service sectors of STD care and OUD treatment.